1. Technical Field
The present invention relates to a rolling bearing having a ceramic film and more particularly to a rolling bearing excellent in insulation performance and a resistance to corrosion and chemicals such as acids and alkalis and a method for manufacturing the same.
2. Background Art
In a rolling bearing which is used for a main motor of a railway vehicle, when a current collector for grounding electric current of the main motor from wheels to a rail is incomplete, the electric current of the main motor flows between the wheels and the rail through inner and outer rings of the rolling bearing and rolling elements thereof. At this time, a discharge is generated between the rolling elements of the rolling bearing and an outer ring rolling surface or an inner ring rolling surface to generate galvanic corrosion at a discharged portion.
As a means for effectively preventing such a galvanic corrosion, it is known that a thermal spray deposit of an insulator such as ceramics is formed on an outer surface of a bearing ring.
Chemical plant equipment such as a plant for producing macromolecular materials, an apparatus for producing liquid crystal films, and the like has various treating apparatuses using various kinds of acids, alkalis, and the like. Rolling bearings used for stirring and feeding use have a problem that they have a comparatively short life because materials composing the bearings contact various kinds of chemicals such as acids, alkalis, and the like and have deterioration such as corrosion, swell, dissolution, decomposition, and the like. Corrosion-resistant and chemical-resistant stainless steel, ceramics, resin, and the like are used for an inner ring, an outer ring, rolling elements, and a retainer. But the stainless steel is not universal and the kind of chemicals such as acids, alkalis, and the like to which the stainless steel can be applied has a limitation. The ceramics have a high resistance to corrosion and chemicals such as acids, alkalis, and the like, but are expensive.
The resin is widely used in recent years in the field of corrosive environment and environment in which various chemicals are used by selecting kinds having a mechanical strength and slidable property and selecting kinds resistant to corrosion and chemicals such as acids, alkalis, and the like.
Conventionally as rolling bearings made of synthetic resin, a rolling bearing (see patent document 1) in which at least an outer ring is made of polyimide, a rolling bearing (see patent document 2) whose bearing ring is made of polyarylene sulfide resin such as polyphenylene sulfide (hereinafter referred to as PPS) having a flexure elastic modulus of 2000 to 6000 MPa, a rolling bearing (see patent document 3) in which lubricating film consisting of polytetrafluoroethylene (hereinafter referred to as PTFE) is formed on the surface of an inner ring and the outer ring where rolling friction or sliding friction is generated are known.
In addition, a rolling bearing (see patent document 4) is known. In the rolling bearing, a film-forming member containing crystalline high-molecular-weight PTFE resin is pressed against the surfaces of components, composing the rolling bearing, on which rolling friction or sliding friction is generated so that both components slide on each other to form a solid lubricating film of the PTFE resin on the surfaces of the components.
But the rolling bearing in which the rolling surface of the inner ring or that of the outer ring is made of resin is inferior to the rolling bearing in which the rolling surface of the inner ring or that of the outer ring is made of steel in resistance to load. By rolling of rolling elements harder than the resin forming the rolling surface, the rolling surface is worn outstandingly and the durability of the rolling bearing is insufficient. Therefore the use of this rolling bearing made of resin is restricted.
As a method for imparting corrosion-resistant and chemical-resistant property to the inner ring and the outer ring made of steel, a method of forming a thermal spray deposit consisting of ceramics or the like having the corrosion-resistant and chemical-resistant property on the outer surface of the bearing ring is known.
But in the method of forming the ceramic layer on the outside surface of the bearing and the end panel thereof by using a thermal spraying technique, to prevent the occurrence of heat-caused tempering of the bearing steel hardened by heat treatment at the time of thermal spraying treatment, it is necessary to form the ceramic layer while a workpiece is being cooled. Thus this method is complicated and has a low productivity. In addition, to form the ceramic layer on the outside surface of the bearing and the end panel thereof by using the thermal spraying method, it is necessary to thermally spray a nickel aluminum layer and the like as a foundation treatment, which causes the deterioration of productivity.
On the other hand, because the ceramic layer obtained by the thermally spraying method is porous, water penetrates into the ceramic layer owing to dew or the like. As a result, the insulation resistance or the resistance to corrosion and chemicals deteriorates. Therefore it is necessary to prevent the penetration of water by sealing pores inside the ceramic layer. As the pore-sealing treatment method, a method (see patent document 5) of using a pore-sealing agent containing at least one kind of a substance selected from the group of synthetic resin, a polymerizable organic solvent, a fluorine-based surface active agent, and an organic silicon compound containing perfluoro group is known. In another known method (see patent document 6), pores are sealed by forming an upper and a lower layer in combination. Pores of the lower layer are sealed with insulating resin having a preferable permeability, whereas pores of the upper layer are sealed with insulating resin having an incomplete permeability. But in using these pore-sealing treatment methods, the manufacturing cost is very high.
In the ceramic layer obtained by the thermally spraying method, even though α alumina is used as the material powder to obtain insulation performance, it transforms into γ alumina having an inferior insulation performance because the thermally spraying step is performed at a high temperature. Therefore this method is required to secure the insulation performance by thickening the film, which causes the manufacturing cost to be high.
Patent document 1: Japanese Patent Application Laid-Open No. 7-279973
Patent document 2: Japanese Patent Application Laid-Open No. 10-47355
Patent document 3: Japanese Patent Application Laid-Open No. 8-93774
Patent document 4: Japanese Patent Application Laid-Open No. 5-106638
Patent document 5: Japanese Patent Application Laid-Open No. 2003-183806
Patent document 6: U.S. Pat. No. 3,009,516